Our Sun is a brilliant cosmic light bulb, shining with 400 trillion trillion watts of power. Yet when compared to the powerhouses known as quasars, the Sun is little more than a pale nightlight. A typical quasar shines a trillion times brighter than the Sun — many times brighter, in fact, than our entire galaxy of stars. Yet all that power comes from a region of space that’s not all that much bigger than our solar system.

The source of this great power is the gravitational field of a supermassive black hole. It draws in stars and enormous clouds of gas. This material forms a rapidly spinning disk around the black hole, like the water circling around a bathtub drain. The gas gets extremely hot, so it emits enormous amounts of energy.

Most of the quasars discovered so far are billions of light-years away, which means we’re seeing them as they looked when the universe was much younger. That suggests that many large galaxies, if not all of them, have quasars at their hearts when they’re born.

Over hundreds of millions of years, though, the black hole at the galaxy’s heart ingests most of the nearby stars and gas. The black hole is still there, but with nothing left to gorge itself on, the quasar shuts down. There may be an occasional flare up when the black hole snacks on a passing star or gas cloud, but nothing like the black hole’s early days — the time when it powered a quasar.